1. Field of the Invention
The present invention relates to a gas transfer pipe arrangement for transferring gas containing droplets of diameters no less than 8 .mu.m at a velocity no less than 6 m/sec, which is employed, for example, in the chemical plant.
2. Description of the Prior Art
In many plants in petroleum refining industries, petrochemical industries and the like, droplets may be generated in the gas flow during processing. Upon transferring the gas flow containing the droplets, it may be necessary, depending on process steps carried out at a destination of the transferred gas, to remove the droplets from the gas flow. For example, at an inlet port of a compressor in the LNG or ethylene plant, it is required to remove no less than 99.9% of droplets having diameters of no less than 8 .mu.m in view of the properties of gas. On the other hand, in a certain reaction system, it is necessary to suppress the amount of droplets contained in the gas flow as much as possible. For achieving this, a special installation, called a knockout drum, a compressor suction drum or the like, having a droplet separating function is provided between adjacent pipes so as to remove the droplets in the gas flow during transfer of the gas.
There have been available various types of droplet separators for such a use, for example, a gravity type in which droplets are separated through gravitational precipitation, a impingement type in which droplets are separated through impingement against a pad which, on the other hand, passes gas therethrough, an inertial force type in which droplets are separated through a difference in specific gravity between gas and droplets utilizing inertial forces, and a centrifugal force type in which droplets are separated through a difference in specific gravity between gas and droplets by applying a centrifugal force to droplets in the gas flow.
FIG. 12 shows an example of the centrifugal force type. In this example, swirl-flow forming means called a tuyere 82 is provided in a separator vessel 81. The tuyere 82 comprises triangular vanes which are arranged at regular intervals so as to form an umbrella shape on the whole. The tuyere 82 is disposed so that an apex thereof is oriented in an axial direction of the separator vessel 81 toward an upstream side relative to the gas flow. Gas containing droplets is supplied into the separator vessel 81 via a gas inlet port 81a connected to an upstream pipe, and then given swirl flows upon passing the tuyere 82. The droplets are separated from the gas due to centrifugal forces caused by the swirl flows. In the figure, 81b denotes a gas outlet port connected to a downstream pipe, and 81c denotes a liquid outlet port.
FIG. 13 shows an example of the inertial force type. In this example, impingement plates called vanes 84 each having, for example, a corrugated shape are arranged at regular intervals in a separator vessel 83. Each of the vanes 84 is disposed vertically and in parallel to a flow passage of gas. In this droplet separator, the gas containing droplets flows zigzag between the adjacent vanes 84. While flowing, inertial forces are applied to droplets having large specific gravities and large diameters so that the droplets deviate from the flow line of the gas and collide against the surfaces of the vanes 84 to form liquid films so as to be separated from the gas flow. In the figure, 84a denotes a gas inlet port, 84b a gas outlet port, and 84c a liquid outlet port. Flow-passage members 85a and 85b are provided between the gas inlet port 84a and the separator vessel 83 and between the separator vessel 83 and the gas outlet port 84b, respectively, to form the flow passage of the gas.
FIG. 14 shows an example of the impingement type. In this example, a mesh pad 87 is provided in a separator vessel 86 at an upper side thereof. In this droplet separator, gas containing droplets is introduced into the separator vessel 86 via a gas inlet port 86a provided substantially at the center of the side wall of the separator vessel 86 and flows upward toward a gas outlet port 86b provided at the top of the separator vessel 86 via the pad 87. Upon passing the pad 87, the droplets collide against the surfaces of the pad 87 to gradually form liquid films which then drop due to the gravity, so that the droplets are separated from the gas flow. In the figure, 86c denotes a liquid outlet port.
In the foregoing droplet separator of any type, however, the applicable range of the gas velocity is small and the inner diameter of the separator vessel is required to be set greater than that of the pipe. Thus, the conventional droplet separator is in the form of a specially prepared large-diameter casing arranged between the adjacent pipes. Accordingly, due to differences in shape and size between the pipe and the casing, the inner diameters are rapidly increased or reduced at a coupling portion therebetween. This increases a pressure drop. Further, as described above, since the shapes of the pipe and the droplet separator differ from each other, the gas flow tends to be disturbed and the droplet locus tends to be disordered so that the allowable range of disturbance of the gas flow and the droplet locus is small. Hence, the designing which can ensure further safety is required, thereby to cause one factor of cost increase.
Further, in the LNG plant, since the inner diameter of the pipe is large, that is, some tens of centimeters to about 1 m, the droplet separator is increased in size to match the large-diameter pipe. Therefore, the cost of the droplet separator itself is increased, and a corresponding large space therefore is required, and further the piping becomes complicate, resulting in cost increase on the whole. Further, since the size increase of the droplet separator causes the size increase of a device for collecting the droplets separated by the droplet separator, a lot of labor and time are required for maintenance, check and recovery.